Automatic transmissions of recent all-wheel drive (AWD) vehicles have become increasingly common as microcomputer technology has continued to advance and has made it possible, with a control computer and a number of control elements, e.g. servo motors, to precision control this engine speed, the connection and the disconnection of an automated clutch between engine and gearbox and clutch members of the gear box, relative to one another so that smooth gear shift is always obtained at the correct speed. The advantage of such types of automatic transmission is that, firstly, with respect to use in AWD vehicles it is simpler, more robust and can be produced at substantially lower costs, and secondly, it has higher efficiency, which results in lower fuel consumption.
In order to perform gear shifts faster, it is known to measure torque for example at the input shaft, so as to be able to control engine output torque in a more optimal way. Torque measurement however, is not easy, since the object that is to be measured (the shaft that transmits the torque) rotates. This makes application of measurement tools such as strain gauges (that are known for measuring small deformations that are the result of the torque exerted on the shaft) difficult and cumbersome.
WO 2001/73389 discloses a sensor for non-contact detection of torque on a shaft by measuring resonance frequency of a string attached to two colours on a shaft. As the shaft is twisted, the string will increase or decrease its pretention, and thereby change its lateral vibration resonance frequency. By measuring the prevailing resonance frequency, it is possible to indirectly determine the torque applied over the shaft.
The known torque measurement systems suffer from various drawbacks, such as slow response times, insufficient accuracy for use in vehicles transmissions, expensive sensor components or complex and/or sensitive sensor systems.
It is an object of the present invention to provide a torque sensor system that is relatively cheap, robust, sufficiently accurate and allows to measure the torque transmitted to a shaft in real time.
To this end, the torque sensor system according to the invention comprises a frame supporting a first shaft and a second shaft, said first shaft comprising first connector means that are connected to second connector means comprised by the second shaft so that a torque is transmittable via the first and second connector means from the first shaft to the second shaft, wherein the first connector means and second connector means are formed so that transmitting a torque induces a reaction force to the frame, wherein the frame is provided with load sensing means that are adapted to measure the reaction force, and an output of the load sensing means represents the transmitted torque.
The present invention is based on the insight that when a torque is transmitted from a first shaft to a second shaft, whereby the connection between the first shaft and second shaft is unbalanced (force being applied to only one side of the shaft), the frame holding the shaft is subjected to a reaction force that is directly proportional to the transmitted torque. A torque can be applied to a shaft by applying a force, that is transverse to the axis direction of the shaft, and at a distance from the axis of the shaft. Two opposite forces can be applied at opposite sides of the shaft, thereby applying a torque to the shaft in a balanced manner. Such balanced application of a torque to the shaft will not induce a reaction force to the frame via the shaft. Alternatively, only one force can be applied to the shaft at a distance from the shaft axis, so that a reaction force will be felt by the frame holding the shaft (since in a stationary assembly the sum of the forces is zero). The reaction force that is the result of an unbalanced transmission of a torque, is directly proportional to the magnitude of the torque. This reaction force is borne by the frame supporting the shaft. This frame can be provided with load sensing means for measuring the reaction force. In this manner, the torque that is transmitted to the second shaft can be measured by measuring the load on the frame. The frame is typically mounted in a fixed position, so that application of load sensing means is easy. Thereby, the invention provides in a torque sensor system that is very simple and consequently relatively cheap, and wherein the torque can be measured in real time.
Preferably, the frame comprises a housing with first supporting means supporting the first shaft and second supporting means supporting the second shaft. In addition, preferably the housing further surrounds the first and second connector means. Connection of the shafts is in mechanical industries, as well as in vehicles often shielded from the environment by making the connection in a housing. The housing ensures that the connection elements, the first connector means and second connector means, are kept free of dirt and other environmental contaminations. Furthermore, the housing shields the connection from persons and animals thereby enhancing the safety of the connection. It will be clear that the housing can be made in one piece as well as an assembly of multiple elements.
Preferably, the load sensing means are positioned adjacent to the first and/or second shaft at a deformation zone of the frame that deforms under application of the reaction force. By placing the load sensing means at a location that is close to one of the shafts (adjacent thereto) and at a deformation zone, where the frame (or the housing forming the frame) deforms under application of the reaction force, the reaction force can be measured with the highest possible accuracy. Thereby, a reliable torque measurement is obtained.
Preferably, the first connector means is a first gear and the second connector means is a second gear, the first and second gear being positioned in an engaging relationship so that a torque is transmittable. Gears are known to be reliable in transmitting a torque from a first to a second shaft. Furthermore, by using gears, an unbalanced transmission of the torque is obtained because two gear wheels engage at a predefined engaging zone where the force (that is hereabove described) is transmitted to the shaft. This force is always directed in substantially the same direction so that the reaction force can be expected at one location of the frame. This makes application of the present invention, whereby the reaction force is measured as an indication of the transmitted torque, more easy.
Preferably the load sensing means comprise at least one strain gauge. Strain gauges are known to be reliable in measuring small deformations of an object. Furthermore, strain gauges are relatively cheap and easy to apply.
As described above, the torque sensor system of the invention is particularly applicable in vehicles, more particularly in all wheel drive (AWD) agricultural vehicles.
The invention further relates to a method for measuring a torque via a torque measurement system comprising a frame supporting a first shaft and a second shaft, the first shaft comprising first connector means that are connected to second connector means comprised by the second shaft, the method comprising transmitting a torque via the first and second connector means from the first shaft to the second shaft; determining a reaction force that is induced to the frame when the torque is transmitted; and measuring the reaction force via load sensing means so that an output of the load sensing means represents the transmitted torque.
According to the method of the invention, the reaction force felt by the frame is determined. The reaction force is a reaction to an unbalanced force that is applied to the second shaft. This unbalanced force is applied to the shaft to transmit a torque from the first shaft to the second shaft. Thereby the measured reaction force is directly proportional to the transmitted torque. Advantages and effects are similar to those described above in relation to the apparatus.
Preferably, after the determining of the reaction force, the method further comprises determining a deformation zone of the frame adjacent to the first and/or second shaft, which deformation zone deforms under application of the reaction force; wherein measuring the reaction force via load sensing means is conducted at the determined deformation zone.
Preferably the determining of the deformation zone is conducted via finite element analysis (FEA). FEA is well known and used in development and engineering environments. Therefore conducting a finite element analysis upon the engineered system where a torque is to be measured, FEA can show the zones in the system where a high stress can be expected. These zones will deform under application of the torque, and are therefore referred to as the deformation zone.